Using a proper controller, while perhaps making you look slightly odd on the bus, means you're not obscuring the screen with your fingers. For console-style action and racing games -- of which there are a great wealth on the Google Play Store, not to mention (ahem) emulators -- this is a huge improvement. You also get the tactile feedback of knowing you've definitely pressed a button, which is sadly lacking when you're just poking a screen.
If you want to play with your PS3 controller on any Android device, you can already do so. It's a little more complicated, and involves downloading an app, but you needn't do anything drastic like root your phone. You can read how to do it in our full guide here, which also explains how to configure games and emulators to work with the controller.
It's taken a very long time for Sony to integrate such an obvious bit of functionality into its phones. It bought out Ericsson to take full control of its smart phone business over two years ago, and its previous gaming effort the Xperia Play, one of its last with Ericsson, was half-baked and very clunky. It's not until this year's waterproof Xperia Z that we've seen a genuinely brilliant mobile from Sony alone.